fn main() {
  let x = 2;
  let y = {
      let x_squared = x * x;
      let x_cube = x_squared * x;

      // 将此表达式赋给 `y`
      x_cube + x_squared + x
  };

  let z = {
      // 分号结束了这个表达式，于是将 `()` 赋给 `z`
      2 * x;
  };

  println!("y is {:?}", y);
  println!("z is {:?}", z);
}
